Dependable Software Systems (OO Protocol Testing)
Dependable Software Systems (OO Protocol Testing) © SERG
Dependable Software Systems
Testing the Protocols of
Classes in
Object-Oriented Programs
Material drawn from [Kirani, Tsai, 1994]
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Method Sequence Specification and Verification in Object-Oriented Protocol Testing - Prof., Study notes of Computer Science
The importance of method sequence specifications in dependable software systems, particularly in object-oriented programs. It explains how regular expressions can be used to represent method sequence specifications and ensures the conformance of implementation with the corresponding method sequence specification. The document also covers test case generation from sequence specifications and inheritance and method sequence specification.
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Dependable Software Systems
Testing the Protocols of
Classes in
Object-Oriented Programs
Material drawn from [Kirani, Tsai, 1994]
Method Sequence Specification
- An object accessing the services of other objects must know the proper interface protocol of the objects.
- The Method Sequence Specification technique documents the correct order in which methods can be invoked.
- Regular Expressions are used to represent method sequence specifications.
Stack Example
- The objects of a Stack class should receive a pop() message only after receiving a push() message.
- Some ordering rules are due to implementation issues: - E.g., objects must receive a constructor message before receiving any other message.
Method Sequence
- Methods(C) is the set of all public methods defined in class C. - For a Stack class the set of methods can be: Methods(Stack) = {push,pop,isempty,isfull,top}
- A method sequence S of C is a finite sequence of methods M of C , (M0.M1. … .Mn) , where Mi (0 <= i <=N) are in set M. - E.g., for the Stack class, a method sequence is: (push.top.pop.isempty)
Example of a Regular Definition
moreoccurancesof a symbol. Theregularexpression can use"*"/" "forspecifyingzero/one or over ( ) { , ,..., }. whereeach isa distinct label,andeach isa regular expression ... 2 2 1 1
! " " " i i n i i n n Methods C l l l l r l r l r l r
Specification of a Simple
Bank Account Class
- Interface methods of the Account class:
- = {Create,Deposit,Open,Withdraw,Close,Delete}
- The regular expression of the method sequence specification for class Account is: ! Create. Open .( Deposit .( Deposit | Withdraw ) ). Close. Delete
- The regular expression is equivalent to the set:
- {(Create.Open.Deposit.Withdraw.Close.Delete), (Create.Open.Deposit.Deposit.Withdraw.Close.Delete), …}
Verification of Implementation
- The method sequence specification of a class specifies the correct sequence usage for all objects of the class.
- But the implementation of a class may contain method invocation sequences that are inconsistent with the method sequence specification.
- It is important to identify and correct all such inconsistencies.
Verification of Implementation (Cont’d)
- We can use manual inspection or static analysis of the implementation to identify inconsistencies.
- Note that pointers, polymorphism, and dynamic binding in OO programs complicates the control-flow analysis. - For dynamic binding of methods to messages, the static analysis must consider all possible methods that can be bound to a message.
Run-time Verification System
- What if all the invalid method sequences are not identified using inspection and static analysis?
- For safety-critical systems it may be necessary to identify all invalid method sequences during execution.
- The run-time verification system helps identify and recover from invalid method invocations.
Run-time Verification System
(Cont’d)
- Each object maintains an access pointer to the method sequence specification of its corresponding class.
- For each method invocation, a check is made for sequence consistency (if the sequence is in the regular language) with respect to the stored sequence specification.
- If the method invoked is not in correct sequence, an exception is raised and handled.
Efficient Algorithm for
Consistency Checking
- We must be able to verify whether one regular expression is the same as another.
- Each regular expression defines a finite automata (FA).
- An FA accepts a set of strings and all of the acceptable strings form a language L.
- If L1 and L2 are the languages represented by two regular expressions, then the two regular expressions are equal if L1=L2.
Algorithm for
Consistency Checking (Cont’d)
- One can verify that L1=L2 by constructing a finite automaton, D1, that satisfies L1 L2. - is the exclusive-or operator.
- If D1 only accepts the empty string, then L1=L2. ! !
Test Case Generation from
Sequence Specification (Cont’d)
- All-node coverage criterion:
- (M1.M2.M3) and (M1.M2.M4)
- All-edge coverage criterion:
- (M1.M2.M3.M3.M4) and (M1.M2.M4.M4.M3) S0 S1 S S S M1 M M M M4 M M M
Test Case Generation from
Sequence Specification (Cont’d)
- For each method in the sequence, data input of each parameter and the expected output must be determined.
- If a method invokes methods of other objects, then during testing test stubs can be used to supply return values.